csv, rrdtool plugin: Initialize a buffer correctly.

csv, rrdtool plugin: Initialize a buffer correctly.

While reading the source code, I found the following:

In csv.c (line 44) and rrdtool.c (line 363) (value_list_to_string) the
following syntax exists:

  memset (buffer, '\0', sizeof (buffer_len));

The sizeof should be removed - assuming that the desire is to zero the buffer
and not the first four (sizeof(int)) bytes.

Based on the code paths - I do not see an information leak - or any security
implications...